Measure of energy and power

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gtvpic
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Measure of energy and power

Post by gtvpic » Thu Apr 18, 2019 9:40 am

Good morning
I have not written in the forum for years, so I take the opportunity to send a friendly greeting to everyone.
I have the need to measure the power and energy of some equipment powered by batteries, the issue is that I intend with my oscilloscope, a 5243, to measure the voltage and intensity of the power supply and to use a pair of mathematical channels to calculate the power and energy .
At the moment the intensity measurement is made by the voltage drop in the terminals of a 0.1 ohm resistor and the voltage is measured directly. Always with the common mass.
In a mathematical channel one is the calculation of the potency so I multiply the channel A x B without more
For the measurement of energy I am doing the integration of the power in time so they would be Wh, but I wanted to be able to make a measurement of the power between the cursors.
The question is: Does anyone know how to measure the energy between cursors?
Finally You can capture hours with the current software version

As always, thank you very much and a special greeting

Gerry
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Re: Measure of energy and power

Post by Gerry » Thu Apr 25, 2019 10:56 am

Hi gtvpic,

Unfortunately, it's difficult to follow the description of what you are doing. because you are using terms like 'intensity' and 'potency', and 'mass' (that are not associated with any electrical properties) and you are not providing key information, such as what is being measure on channels A and B.

What I can tell you is that Energy is the work done in the time taken to do it, or Energy = Power x Time. Assuming that you are calculating Power by multiplying Current on one channel by Voltage on the other in a Math channel, then integrating the Power Math Channel will give you the area under the curve (which is average Power x Time), which is what I believe you are doing.

So, to give you an answer to what appears to be the one question you are asking, there is no way to include the cursor positions in the Math channel calculation within PicoScope 6. However, if the Math channel is linear then you can get the Energy by just subtracting the smaller value Time ruler measurement from the other, and then multiplying the time difference by the value of Power at the mid-point between the 2 rulers. If it's not linear, then you can export the Math Channel and Measurements (using the automation command: picoscope.com /a Measurements.csv?) and then do the calculation externally (e.g. in Excel).

Regards,

Gerry
Gerry
Technical Specialist

gtvpic
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Joined: Wed Apr 17, 2019 2:09 pm

Re: Measure of energy and power

Post by gtvpic » Fri Apr 26, 2019 6:57 am

Thank you very much for the reply.
Effectively I do not explain it totally well, so I will try to be more precise this time
I need to measure the power and energy absorbed by a team between the selected time periods.
Consumption is not linear and the measurement has to be done for a period of approximately 4 hours.
The feeding is carried out at 12Vdc with an intensity that ranges from 0.5 to 6.5A.
The power supply of the system is a 12V 16Ah lead acid battery

In Channel A, the battery supply voltage is measured directly from the terminals. This measure is correct and does not present any problem

In Channel B, the circuit current is measured, this is done with a resistance 0.1 ohm 0.1% accuracy. This generates a voltage drop in its terminals that is measured and an X10 probe is applied so that the reading is Amperes. This measure is correct and does not present any problem.

In a mathematical channel I calculate the power multiplying the value of the channel A x B so that I get the instantaneous power in watts. This measure also I think is correct and works properly. I DO NOT have adequate equipment to carry out the verification but the values ​​are very reasonable.

Up to this point everything seems to work well and the measurement values ​​are correct compared to external equipment.

In Another mathematical channel, I try to calculate the energy consumed in the selected period of time between the cursors, this is what is not really done and is the real reason for the query. What I am doing is integrating the power but the result that is presented is not correct or at least it is not an adequate value to the measures that I am doing.
How can I make such a measurement of Wh between the position of the cursors?


I would also have to be able to measure the ampere hours of battery supply but this will no longer be possible with this equipment. It's possible?

Thank you so much

Gerry
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Re: Measure of energy and power

Post by Gerry » Mon Apr 29, 2019 10:17 am

Hi gtvpic,

I think that the issue here may be to do with the way the integral works. You have to be very careful about how you set the Minimum and Maximum values for the range when using an integral and working with DC currents/voltages, because an error can make the results far too small or too large to see. Also, over long periods of capture, the slightest offset can throw your results off, due to the accumulated error over time. If you can post a psdata file of what you have captured with the settings you are using, we can have a look at it and see where the setup error is.

Also, regarding Ampere Hours, the same principle applies in that to multiply the current by the time period for which the current is drawn you can integrate the current (area under the curve = average current x time).

Regards,

Gerry
Gerry
Technical Specialist

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